Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (7,238)	$ (17,058)
Adjustments to reconcile net loss to net cash used in operations:
Depreciation and amortization	488	1,103
Gain on disposal of property and equipment	(450)	0
Share-based compensation expense	389	619
Non-cash interest expense	3	0
Inventory write-downs	168	852
Change in:
Accounts receivable, net	1,079	(2,048)
Costs and estimated earnings in excess of billings on uncompleted contracts	0	987
Inventory	24	203
Other current and non-current assets	551	336
Accounts payable	(355)	(412)
Accrued liabilities	(1,544)	(608)
Deferred revenue	(21)	0
Billings on uncompleted contracts in excess of related costs	0	101
Other currrent liabilities	(1,139)	(112)
Operating lease liabilities	(325)	(321)
Net cash used in operating activities	(8,370)	(16,358)
Cash flows from investing activities
Proceeds on sale of property and equipment	525	0
Purchases of property and equipment	(94)	(513)
Net cash provided by (used in) investing activities	431	(513)
Cash flows from financing activities
Principal payments under finance leases	(13)	(9)
Increase in long-term debt	1,571	0
Net proceeds from issuance of common stock	8,349	7,728
Net cash provided by financing activities	9,907	7,719
Change in cash and cash equivalents, and restricted cash	1,968	(9,152)
Cash, cash equivalents and restricted cash at beginning of period	6,272	14,201
Cash, cash equivalents and restricted cash at end of period	8,240	5,049
Supplemental schedule of non-cash investing and financing activities
Non-cash additions to property and equipment	19	15
Issuance of common stock for commitment fee	$ 0	$ 258